1. Field of the Invention
The present invention relates to a diaphragm mechanism of a zoom lens barrel used in an interchangeable lens camera. More precisely, it relates to an apparatus for driving a diaphragm mechanism of a zoom lens barrel in which the diaphragm mechanism is provided on a movable front lens group in front of a rearmost lens group, from a camera body side.
2. Description of Related Art
In a known zoom lens barrel for a single lens reflex camera including, for example, three lens groups, a diaphragm mechanism is usually provided on the second lens group located in front of the rearmost (third) lens group.
There are two types of diaphragm mechanisms, i.e., a normally open type and a normally closed type in which the diaphragm (aperture) is biased to be opened and closed when the lens barrel is detached from the camera body, respectively. In either type, the diaphragm which is fully opened in a normal state stops-down to a predetermined diaphragm value when the shutter is released. To this end, the zoom lens barrel is provided with an association mechanism which is associated with a drive member of the camera body. The association mechanism is usually comprised of an intermediate drive transmitting member (lever) which is provided on a supporting lens frame of the second lens group, on which the diaphragm mechanism is provided to actuate the diaphragm mechanism, and a diaphragm driving member (lever) which is provided on the rear portion of the lens barrel to be associated with the drive member of the camera body. The diaphragm driving member of the lens barrel is functionally connected to the intermediate drive transmitting member. Consequently, in the known mechanism, it is necessary to lengthen the arm of the diaphragm driving member (lever) and/or the intermediate drive transmitting member (lever) in order to increase the displacement of the second lens group. In such case, however, the diaphragm driving lever or the intermediate drive transmitting lever tends to be inclined or deflected due to the increased arm length thereof, thus resulting in an inaccurate or unstable control of the diaphragm. Furthermore, it is necessary to provide a large space (e.g., recess or cut-away portion) in which the diaphragm driving lever or the intermediate drive transmitting lever can be displaced This causes harmful internal reflection or allows passage of stray light.